Recently a new class of thermoelastic sulfonated polymers has been described in a number of U.S. patents. These sulfonated polymers are derived from polymeric materials having olefinic unsaturation, especially elastomeric polymers such as Butyl and EPDM rubbers. U.S. Pat. No. 3,642,728, herein incorporated by reference, teaches a method of selective sulfonation of olefinic unsaturation sites of an elastomeric polymer to form an acid form of a sulfonated elastomeric polymer. The olefinic sites of the elastomeric polymer are sulfonated by means of a complex of a sulfur trioxide donor and a Lewis base. The SO.sub.3 H groups of the sulfonated elastomer can be readily neutralized with a basic material to form an ionically crosslinked elastomer at room temperature. However, these ionically crosslinked elastomers may be processed like a conventional thermoplastic at elevated temperatures under a shear force in the presence of selected preferential plasticizers which dissipate the ionic associations at the elevated temperatures thereby creating a reprocessable elastomer. The basic materials used as neutralizing agents are selected from organic amines or basic materials selected from Groups I, II, III, IV, V, VIB, VIIB, and VIII and mixtures thereof of the Periodic Table of Elements.
U.S. Pat. No. 3,836,511, herein incorporated by reference, teaches an improved process for the sulfonation of the olefinic sites of the elastomeric polymer wherein the improved sulfonating agent is selected from acetyl sulfate, propionyl sulfate and butyryl sulfate. The neutralizing agents employed to neutralize the acid form of the sulfonated elastomeric polymers are organic amines.
U.S. Pat. No. 3,870,841, herein incorporated by reference teaches a method of plasticization of the polymeric backbone of a neutralized sulfonated plastic polymer by means of a polymer chain plasticizer which is a liquid compound having a boiling point of at least about 120.degree. F. The polymer chain plasticizer is selected from a dialkyl phthalate, a process oil or an organic acid ester. Additionally, a domain plasticizer can be incorporated into the composition, wherein the domain plasticizer reversibly disrupts the association of the sulfonate groups at a temperature of forming.
U.S. Pat. No. 3,847,854, herein incorporated by reference teaches a method of improving the processability of neutralized sulfonated elastomeric polymers by the addition of a preferential plasticizer which has at least one functional constituent which exhibits a bond moment whose absolute value is at least 0.6 Debye and must be a liquid at the desired processing temperature of the neutralized sulfonated elastomeric polymer.
U.S. Pat. No. 4,151,137, herein incorporated by reference, teaches blend compositions which comprise 100 parts of a neutralized sulfonated EPDM terpolymer, less than about 200 parts per hundred of a paraffinic, low polarity process oil, about 25 to about 200 parts per hundred of an amorphous silica filler, and a preferential plasticizer at about less than 50 parts per hundred based on 100 parts of the sulfonated elastomeric polymer. The compositions may also include a crystalline polyolefinic thermoplastic at less than about 100 parts by weight per 100 parts of sulfonated polymer. These compositions are used for elastomeric articles. This patent teaches that the compositions of the aforementioned patents (U.S. Pat. Nos. 3,642,728; 3,836,511; 3,870,841 and 3,847,854) possess either unsuitable rheological or physical properties for the applications envisioned. For example, their high melt viscosity and melt elasticity make injection molding and extrusion difficult if not impossible. They are generally processable only by compression molding and have unsuitable physical properties for such major applications as footwear and garden hose wherein excellent resilience, dimensional stability, excellent low and high temperature flexibility, excellent flex fatigue and excellent abrasion are needed.
In contrast, the compositions of U.S. Pat. No. 4,151,137 are taught as overcoming the deficiencies of the compositions of the aforementioned U.S. patents from both a rheological and physical aspect and as having desirable rheological and physical properties for the manufacture of elastomeric articles such as elastomeric footwear or garden hose.
A common method of construction for footwear, in particular for casual type footwear, consists of the formation of two separate pieces which subsequently are bonded together with an adhesive. The two pieces are an upper and a lower member. The upper member, which encloses the foot, can be constructed from a variety of materials. Commonly used materials are leather, fabrics and fabrics coated with polymeric resins such as flexible polyvinyl chloride. The lower member, the wearing surface of the shoe, is a molded or die-cut sole and heel and is commonly made from an elastomeric material.
In a prevalent construction method, the sole and heel are one unit generally referred to as a "unit sole". In a particularly efficient production method, the unit sole is injection molded from a thermoplastic elastomer. In this method, no vulcanization is required, scrap can be recycled and high rates of production can be achieved.
In the shoe industry, the technology of adhering the unit sole to the upper member has become highly developed. Adhesive systems have been designed specifically for these applications. Particularly effective adhesives are based on polyurethane resins. These adhesives are commonly one component system consisting of a fully reacted polyurethane elastomer risin in a volatile solvent. A typical example of such an adhesive is Upaco 2400 supplied by Upaco Adhesives, Inc., Nashua, N.H.
In the prevalent method of use the adhesive cement is applied to the surfaces of the upper and lower member which are to be adhered. The solvent is allowed to evaporate and the parts are then heated to a recommended temperature to soften the polyurethane resin. The two surfaces are then pressed together under moderate pressure whereby the polyurethane resin amalgamates and on cooling forms a strong bond which adheres the two members to form the finished shoe. Acceptable service life of this type of footwear requires that the adhesive bond be strong and durable. While polyurethanes have the required strength, they do not adhere equally well to all substrates. In particular, the polyurethanes do not adhere well to non-polar hydrocarbon polymer surfaces.
With the introduction to the industry of hydrocarbon type thermoplastic elastomers such as styrene/butadiene/styrene triblock copolymer resins for unit soles, primers and pretreatments were developed to effectively modify the surface so that an acceptable bond could be achieved with polyurethane type adhesives. A typical example of such primers is Upaco 3213 also supplied by Upaco Adhesives, Inc.
The compositions described in the prior art patent U.S. Pat. No. 4,151,137 possess an exceptional balance of properties for unit soles such as excellent low and elevated temperature flexibility, excellent abrasion resistance, excellent flex fatigue, good resilience, resistance to oils and detergents and rubber-like feel and appearance. However, they have proved to be deficient in adhesive bonding capability using the adhesive systems required for the application even when treated with the primers developed for hydrocarbon-type thermoplastic elastomers. What is required are compositions which provide adhesive bond strength substantially superior to the prior art compositions and serviceable in the unit sole application using the typical primer/adhesive systems just described.